Retrospectively, the first spinfoam model was constructed by Ponzano and Regge [1]} and defines a discrete topologically-invariant path integral for three space-time dimensional gravity in Euclidean signature with vanishing cosmological constant [2]}, [3]}, [4]}.
Let us underline that this is not a Wick-rotated path integral but it is truly the quantum theory of a positive signature metric with probability amplitudes in \(\exp [iS_{grav}]\) .
A posteriori, the Ponzano-Regge model has been understood as the discretized path integral for 3D gravity written in terms of veirbein-connection variables as a topological BF theory with gauge group \(\mathrm {SU}(2)\)  [3]}.
There exists a Lorentzian version of this model based on the \(\mathrm {SU}(1,1)\)  gauge group [6]}, [7]}, [8]}, [9]}. One can also take into account a non-vanishing cosmological constant through a q-deformation of the gauge group [10]}, [11]}, [12]}. This yields the Turaev-Viro topological invariant when the quantum deformation parameter \(q\)  is a root of unity [13]}. Through this relation, the Ponzano-Regge state-sum has been understood as a special case of the Reshetikhin-Turaev invariants [14]} and thereby related to the quantization of 3D gravity as a Chern-Simons theory as advocated by Witten [15]}.
